1. Field of the Invention
The present invention relates to a hydraulic tappet comprising: a bottomed cylindrical body; a plunger slidably fitted in the body; a check valve mounted at one end of the plunger so that the check valve is interposed between a high-pressure chamber and an oil chamber, the high-pressure chamber being formed between a closed end of the body and one end of the plunger, the oil chamber formed within the plunger; a return spring mounted between the body and the plunger to exhibit a spring force for biasing the plunger in a direction to increase the volume of the high-pressure chamber.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2001-73723 discloses a valve-operating system for an internal combustion engine in which a hydraulic tappet is mounted on a rocker arm following a cam of a camshaft so that the hydraulic tappet is interposed between the rocker arm and an engine valve. In this valve-operating system, a return spring having a coil shape mounted between a body and a plunger to exhibit a spring force for biasing the plunger in a direction to increase the volume of a high-pressure chamber is accommodated in the high-pressure chamber.
In order to reduce the size of the hydraulic tappet, it is necessary to reduce the volume of the high-pressure chamber to decrease the flow rate of oil generated due to the operation of the high-pressure chamber. In the conventional valve-operating system, however, the return spring is accommodated in the high-pressure chamber, leading to a limitation in reducing the volume of the high-pressure chamber, which is an obstacle to the downsizing of the hydraulic tappet.